Running application servers on your z/OS® system
often requires a high amount
of virtual storage. Because virtual storage uses real storage as backup,
real
storage usage might also be high. Therefore make sure that you do
not underestimate
the amount of virtual storage that you allocate to running your application
servers.
Before you begin
Determine your application
server virtual storage requirements based
on the number of application servers you are running and the number
of requests
that each of these servers handles.
About this task
Perform one or
more of the following steps if you need to improve
client request throughput.
Procedure
- Allocate additional
virtual storage. The setting of REGION on
the JCL for the proc controls the amount of virtual storage available
to a
z/OS address
space. The default values for the WebSphere® Application
Server controller
and servant are set to zero, which tells the operating system to allocate
all the available region (close to 2GB). You can limit the amount
of virtual
storage allocated by setting the REGION parameter
to a
value other than zero. The size of the JVM heap is the most important
factor
when determining the setting of the REGION parameter.
You
should only need to set the REGION to something
other than
zero when the JVM heap size is very large. The z/OS operating
system allocates user storage
from the bottom of the address space, which is where the JVM heap
is allocated,
and system storage from the top. System abends can occur when the
system
tries to obtain virtual storage and none is available. A non-zero REGION parameter
setting prevents this from occurring by preserving storage at the
top of the
address space for system use. In almost all cases running with the
default REGION will
be satisfactory.
Note: For more information on REGION=0M and
IEFUSI, please see Installing your application serving environment
ection
of the information center.
- Convert
application servers with high virtual storage usage to
run in 64-bit mode. Running an application server in 64-bit
mode
allows you to specify larger JVM heap sizes.
- Convert
deployment mangers, that are managing cells in which very
large applications are deployed, to run in 64-bit mode.
- Allocate additional real storage. The total
amount of
real storage that your system requires depends on the number of servers
you
are running and the size of the JVM heaps for each server. You should
allocate
at least 512MB of real storage for a small configuration.
Recommendation: Sometimes in a heavy use environment,
2GB of central storage is not enough to handle the real storage demands
of
a high volume Java application. In this situation,
you might want
to configure your servers to run in 64-bit mode. Running your servers
in 64-bit
mode gives you the ability to dedicate more central storage to the
LPAR, and
the ability to define more than 2GB of central storage. When you configure
your servers to run in 64-bit mode, all of the storage is defined
as central
storage.
The z/OS operating
system running on a zSeries® processor always runs
in 64-bit mode. If
you are using a non-zSeries processors, or are running your servers
in 31-bit
mode, you can minimize paging by defining more expanded storage.